1. Field of the Invention
The present invention relates to a method in underground coal mining for separating the upper coal of a seam from the roof during the advancement of the upper sliding cap of a support frame, wherein the front edge of the cap is forced in a plane of the cap between the upper coal to be separated and the rock from which the coal is to be separated.
2. Description of the Prior Art
In underground mining, coal may be extracted in accordance with the longwall working method utilizing, for example, a coal plane which is moved at a certain height level between roof and footwall. In the ideal case, the coal is always separated to the level of the roof. However, in practice, geological disturbances may have the result that upper coal or residual coal remains attached to the roof. With advancing extraction, each individual support frame must be advanced in the longwall by actuating, for example, a walking legs mechanism which connects the support conveyor with the support frame. This advance movement is impaired or prevented by any upper coal remaining attached to the roof because the front edge of the cap of the support frame presses in the plane of the roof between the upper coal and the rock and the pressure may not be sufficient for separating the upper coal.
In order to facilitate the separation of the upper coal from the roof, the cap may include a wedge-type arrangement.
Similar problems occur in shield-type support frames with packing caps which are advanced together with the support conveyor in order to close open spaces. This is because any remaining residual coal may block the advancement of the packing or sliding cap. To ensure that this cap contributes to the separation of the upper coal, this cap can be provided with a separating wedge or a tearing ledge. However, it happens again and again that the force available for advancing the cap is not sufficient for separating the upper coal.
It is, therefore, the primary object of the present invention to further develop a method of the above-described type in such a way that the separation of the upper coal is facilitated or made possible, without requiring complicated or expensive apparatus.